Catalytic production of maleic and phthalic anhydride



United States Patent 3,106,569 CATALYTIC PRODUQ'HQN 0F MALEIC ANDPHTHALHC ANHYDE Warn D. Robinson, Webster Groves, Mo, assignor toMonsanto Chemical Company, St. Louis, Mo., a corporation of Delaware NoDrawing. Griginal application Dec. 31, 1957, Ser. No. 706,287. Dividedand this application Dec. 3, 1959, Ser. No. 856,919

9 Claims. (Cl. 260346.4)

This invention relates to the catalytic oxidation of organic compoundsand more particularly to the vapor phase catalytic oxidation of organiccompounds in the preparation of organic dicarboxylic acids andanhydrides, such as maleic acid, maleic anhydride, phthalic acid andphthalic anhydride.

This application is a division of copending application Serial Number706,287, filed December 31, 1957, now abandoned, which is acontinuation-in-part of application Serial Number 626,591, filedDecember 9, 1956, now abandoned, which is a cont-inuation-in-part ofapplication Serial Number 406,580, filed January 27, 1954, nowabandoned. The principal objects of this invention are to provide animproved vanadium containing catalyst for the vapor phase oxidation oforganic chemical compounds. A more specific object of this invention isto provide an improved vanadium containing catalyst for the vapor phaseoxidation of organic chemical compounds to maleic acid and/or maleicanhydride, such as the oxidation of, for example, the butanes, thebutenes, the pentanes, the pentenes, the hexanes, the heptanes, theheptenes, the octanes and the octenes, cvclopentane,cyclopentene, cyclohexane, cyclohexene, benezene, toluene, phenol, crotonaldehyde crotonicacid, furan, furfuryl alcohol, furfural, oxymethyl furfural andturpentine oil to maleic acid and/ or maleic anhydride; and for thevapor phase oxidation of such organic compounds to phthalic acid and/oranhydride as, for example, the oxidation of naphthalene, the xylenes,phenanthrene, indene, and bicyclononadienes, among others. The vaporphase oxidation of the above organic compounds to dicarboxylic acidsand/or anhydrides is well known by those skilled in the art.

The vapor phase catalytic oxidation of the above organic compounds isaccomplished by a process in which a gaseous reaction mixture of theorganic compound and an oxygen containing gas is passed in contact witha catalyst contact mass containing metallic oxides. This vapor phaseoxidation process is well known to those skilled in the ant and manymetallic oxides have been suggested as catalysts for use in suchprocesses either alone or in various combinations. The oxidation ofmaterials oxidizable to maleic acid or anhydride and phthalic acid oranhydride has presented problems not encountered in the catalyticformation of other organic materials. A number of catalytic materialsproposed for the oxidation of other organic materials such as theoxidation of alcohols to acids are active to some degree to promote theoxidation of, for example, benzene to maleic anhydride or naphthalene tophthalic anhydride. However, the yields obtained of maleic anhydride orphthalic anhydride are too low and either an excessive proportion of theoxidizable material passes uncharged or is completely oxidized to carbondioxide and water. Also in the case of the vapor phase oxidation ofbenzene, some proposed catalyst combinations result in the formation ofexcessive quantities of lower aliphatic acids.

Chief among the catalysts successfully employed in the oxidation ofmaterials oxidizable to maleic acid and anhydride and phthalic acid andanhydride are molybdenum and vanadium which are usually employed in the7 3,106,569 Patented Oct. 8, 1963 ice form of their oxides. Often othermaterials are added to increase the effectiveness of molybdenum orvanadium. Catalyst [materials containing vanadium or molybdenum togetherwith other promoters, stabilizers or the like, are many times referredto as vanadium or molybdenum catalysts depending, of course, on themajor component of the material. For example, a two-component mixturecontaining more than 50% vanadium is referred to as a vanadium catalyst.Likewise, a three-component catalyst containing 40% or more vanadium and30% or less of each of the other components is referred to as vanadiumcatalyst. This invention pertains to vanadium containing catalystsincluding such catalysts in which vanadium is the only metal componentas well as those which vanadium is a major as well as a minor componentand a method of preparing these catalysts especially for use inprocesses for preparing maleic anhydnide and/or acid and phthalicanhydride and/ or acid by the controlled vapor phase oxidation ofmaterials oxidizable to maleic acid and/or anhydride and materialsoxidizable to phthalic anhydride and/ or acid with an oxygencontaininggas.

Generally the catalytic mixture is supported on some inert base orsupport which acts as a distender. These bases are generally much lowerin cost than are the metallic components of the catalyst and hence helpreduce the cost of the resulting catalytic contact mass. Also, since theefficiency of the catalyst seems to be to some extent a function of thesurface area, the inert base or support gives the catalytic contact massa greater surface area than that otherwise would be possessed by thecatalyst. Impregnating a porous inert support with a catalytic materialin such a manner as to provide a porous catalytic contact mass alsoenhances the efficiency of the catalytic rnixture by exposing a maximumof active surface area to the gaseous reaction mixture.

A common method of preparing a vanadium oxide containing catalyticcontact mass is to coat and/ or impregnate particles of the inertcarrier support with a solution containing a vanadium catalyticcomposition which can be readily converted to the oxide or oxides ofvanadium. The carrier thus treated is heated to remove the solvent andthereby produce a coating of the vanadium containing catalyst on and inthe carrier. The vanadium containing composition is thenconvertedchemically to the oxide or oxides of vanadium. When a promoter orstabilizer is to be employed with vanadium they are added to thesolution containing the vanadium compound and the entire mixtureemployed to coat or impregnate the carrier. When such promoter orstabilizer materials are employed the resulting catalyst on the carrieris generally a mixture of oxides. Various catalytic contact massesheretofore disclosed as being useful to promote vapor phase oxidation ofmaterials oxidizable to maleic acid and/or anhydride and phthalic acidand/or anhydride result in yields which are not satisfactory, usuallyranging from about 33% to about 40% of the amount of the acid oranhydride theoretically obtainable from the organic material beingoxidized. For example, when the catalytic contact masses heretoforedisclosed are employed in the oxidation of benzene the yield of maleicacid per pounds of benzene changed is about 50 to about 60 pounds afitera period of stabilized oxidation condition is obtained. Some catalyticcontact masses heretofore proposed produce a higher initial yield butvery readily degenerate in a matter of a relatively short time to theyields described above. It is readily apparent that the variouscatalytic contact masses heretofore proposed ane highly inefiicient.

The inefficiency of processes for controlled catalytic oxidation oforganic compounds, especially the controlled catalytic oxidation oforganic chemical compounds to maleic anhydride and/or phthalicanhydride, is believed to be due to a drop off of activity of thecatalytic materials. This dropping off of activity has been attributedto either removal of one of the catalyst components by sublimation orvaporization or a loss of catalytic area. There have been attempts toovercome the physical removal of part of the catalytic mixture bylowering the oxidation reaction temperature. Although such amodification does reduce the loss of certain components of the catalyst,the activity of the catalytic contact mass is also decreased thereby. Italso appears that in general the catalytic contact masses heretoforeproposed have a relatively short catalyst life, less than 1,000 hours.Thus, it is not economically feasible to employ any of these catalystsfor more than about 1,000 hours of continuous operation.

According to the present invention, it has been found that a catalystcontaining oxides of vanadium, molybdenum and titanium in the proportionrepresented by the atomic percentages of each of said metals of fromabout 50 to about 90 atomic percent of vanadium, from about to about 45atomic percent of molybdenum and from about 2 to about 30 atomic percentof titanium based on the sum of the atomic weights of said metalspresent, has an exceedingly long catalyst life and produces highconsistent yields for thousands of hours. The preferred catalysts ofthis invention are those having from 60 to 86 atomic percent vanadium, 5to 30 atomic percent molybdenum, and 8 to 10 atomic percent titanium. Byatomic percent, as employed in the specification and claims, is meantthe fractional part (expressed as percent of the atomic sum) of themetals present.

It also has been discovered that the use of the above described catalystin the controlled vapor phase oxidation of organic chemical compoundswith an oxygen containing gas such as air, air enriched With oxygen andthe like, at elevated temperatures, e.g. of from 300 to 600 C. andpreferably from 350 to 450 C., and at a pressure of from atmosphericpressure to elevated pressures such as 50 pounds per square inch orhigher results in the production of consistently high yields ofdicarboxylic acids and anhydrides thereof such as maleic acid, maleicanhydride, phthalic acid and citraconic acid for many thousands of hoursof continuous operation. Also by employing slightly modified conditionsof temperature, pressure and oxygen content, alcohols may be oxidized toaldehydes and aliphatic monocarboxylic acids. More specifically, byemploying the catalyst of this invention according to the process ofthis invention, exceedingly high yields of maleic acid in the range offrom 90 to 100 or more pounds per 100 pounds of benzene charged can beachieved, or yields of phthalic anhydride above 80 pounds per 100 poundsof naphthalene charged can be achieved, or yields of maleic anhydride inexcess of 80 pounds per 100 pounds of butadiene-l,3 charged can beachieved, or yields of maleic anhydride in excess of about 50 pounds per100 pounds of furfural or crotonaldehyde can be achieved.

The catalyst mass of this invention containing the components describedabove does not possess the objectionable properties possessed by themetallic oxide catalysts heretofore employed, rather the catalyst ofthis invention is exceedingly stable, is far more active and itsactivity is constant over long periods of continuous use. The catalystcontact masses produced from the catalyst of this invention possessphysical and catalytic stability greater than that which was possible toachieve with the catalysts heretofore proposed for the oxidation ofmaterials oxidizable to maleic anhydride, maleic acid, phthalicanhydride, phthalic acid and other organic acid anhydrides and organicacids.

The process of this invention employing the new catalyst hereinbeforedescribed reduces the free or unreacted material being oxidized presentin the off-gases through the extremely high conversion to the desiredproduct so that the gases after the removal of the desired producttherefrom can be vented to the atmosphere Without an appreciable loss ofthe starting material. For example, in the oxidation of benzene tomaleic anhydride the gases remaining after the recovery of maleicanhydride can be vented to the atmosphere Without an appreciable loss ofbenzene. In contrast to this, the off-gases from many of the processesheretofore proposed for the oxidation of organic chemical compounds toaldehydes, organic acids and organic acid anhydrides containedconsiderable quantities of the starting material and obviously could notbe vented to the atmosphere without increasing processing costs due tothe loss of appreciable quantities of the starting raw material.

It is desirable to support the catalytic material of this invention uponsome mechanically strong and chemically inert body which has thecombined effect of greatly extending the exposed surface of the catalystand functioning as the support therefor to prevent mechanicaldisintegration of the catalyst into dust.

Among the substances which have been suggested as catalyst carriers arethe following: ordinary unglazed porcelain, pumice, asbestos, and shapedpieces of metal which can be coated with a sufiicient layer of catalystso that the metal itself acts as a support and does not influence in anyway the catalytic activity of the coating, except perhaps by extendingthe surface as a catalyst support normally functions. Also with respectto catalytic inactivity toward chemical reactions and resistance tofusion by heat, silica in a porous form is recognized as being ofexceptional merit as a catalyst carrier. Any of these or other inertmaterials such as for example, quartz fragments, alumina, corundum,diatomaceous stones, among others, can be employed as a carrier for thecatalyst of this invention.

An exceedingly useful carrier or support for the catalyst of thisinvention employed to prepare the catalytic contact mass used in theprocess of this invention is porous material prepared by mixing finelyground silica or material rich in silica with finely ground refractoryglass of which the Pyrex type is suitable and then heating said mixtureto a temperature sufficient to soften the glass. These carriers aremechanically very hard and strong, chemically inert when used in thecatalytic oxidation of organic materials, especially when very thinlycoated, and are of sutficient porosity to absorb or otherwise hold andretain a catalytic material in relatively permanent association.

A highly convenient method of preparing this particular carrier of thepreferred inert carriers comprises adding to the pulverized silica andglass a temporary and volatile binder which holds the material as acoherent mass during the preliminary stages of forming but disappearsduring calcination.

Finely divided pumice of to 300 mesh (US. Standard sieve size) is alsoan exceedingly useful catalyst support where the catalytic contact massis to be employed as a fluid catalyst. Larger particles can be usedwhere the catalyst contact mass is utilized as a fixed bed. Quartzfragments are also extremely useful as a catalyst carrier for thecatalyst of this invention for fixed bed catalytic contact masses. Smallshaped pieces of metal and metal turnings, to which a relatively thickuniform continuous coating of catalyst can be applied, are also suitableas catalyst carriers for the catalyst of this invention for fixed bedcatalyst contact masses. The use of these and other carriers will behereinafter illustrated.

The catalytic material of this invention may be applied to the abovedescribed carrier particles in any convenient manner. One methodinvolves forming a solution of the soluble salts of vanadium andmolybdenum and dispersing therein titanium oxide and then applying theresulting mixture to the particles by spraying or dipping to give ahighly intimate and permanent associationbetween the metallic compoundsand the carrier. A second method which may be conveniently employedinvolves merely dusting the particles with the catalyst of thisinvention in a finely ground pulverulent state. A third method which canbe employed involves preparing an aqueous paste comprising water solublesalts of vanadium and molybdenum which can be converted to vanadium andmolybdenum oxides and titanium oxide so that the paste contains thesethree metals in the proportions hereinbefore defined, mixing said pastetogether with carrier particles in any suitable equipment to provide auniform deposit of the paste on the particles. When either of thesethree methods is employed the catalyst may become intimately bonded tothe carrier. Then the coated particles are subjected to heat treatmentat a temperature suflicient to convert the salts of vanadium andmolybdenum to their oxides. This may be accomplished in the presence ofair, oxygen containing gas or even in the presence of an inert gas,especially where the salts of Vanadium and molybdenum will readily breakdown to their oxides merely on heating and require no oxygen to convertthem to the desired oxides. Other methods of preparing vanadium oxidecatalysts, as for example by impregnation, precipitation, evaporation,extrusion, pelletizing a mixture, etc., which are known to those skilledin the art, can be used to prepare the catalyst compositions of thisinvention.

Suitable vanadium compounds convertible to oxides of vanadium uponheating under oxidation conditions include ammonium vanadate and suchvanadium containing organic chemical compounds as amine salts of vanadicacid, amidine salts of vanadic acids, esters of vanadic acid andvanadium complex salts of organic and inorganic acids. Specific vanadiumcontaining organic chemical compounds include but are not limited tovanadium lactate, cyclohexyl vanada-te, benzyl vanadate, guanidinevanadate and diphenyl guanidine vanadate. Similarly the suitablemolybdenum compounds convertible to oxides thereof upon heating underoxidation conditions include ammonium molybdate and such molybdenumcontaining organic compounds as amine salts of mol-ybdic acid, amidinesalts of molybdic acid, esters of molybdic acids and molybdenum complexsalts of organic and inorganic acids.

The following examples are illustrative of the present invention but arenot to be construed as limitations there EXAMPLE I A paste is preparedfrom a mixture containing 38.2 parts by weight of ammonium vanadate,which have been previously reduced with S 12.8 pants by weight ofunreduced ammonium vanadate and 3.9 parts by weight of titanium dioxideslurried with 250 ml. of water made definitely alkaline withconcentrated aqueous ammonium hydroxide solution.

To this alkaline slurry there is added an aqueous solution containing9.5 grams of ammonium paramolybdate [(NHg MO O fifi O] in 50 ml. ofwater and the resulting mixture stirred and heated to 80 C. The metalspresent in this composition arein the proportion of 81 atomic percentvanadium, l0 atomic percent molybdenum and 9 atomic percent titanium.

To this paste there is added 250 cc. of porous carrier particles ofsilica and refractory glass in the form of small cylinders having anaxis of about 0.16 inch in length and 0.16 inch in diameter, hereinafterreferred to as 0.16 inch pellets. The entire mass is stirred slowlywhile driving off the water on a steam bath. The coated pellets are thendried.

EXAMPLE II To an aqueous mixture prepared by combining 38.2 grams ofreduced ammonium vanadate, 12.8 grams of unreduced ammonium vanadate and3.9 grams of titanium dioxide in 250 ml. of water made alkaline withammonium hydroxide, there is added 9.5 grains of ainmonium paramolybdatein 50 ml. of Water. The resulting mixture is stirred and heated on asteam bath to about C. Thereafter 250 cc. of 0.16 inch pellets heated toabout 80 C. are added and the entire mass is stirred and heated on thestream bath until it appears dry. The coated pellets are air dried.

EXAMPLE III An aqueous slurry made alkaline with ammonium hydroxide andcontaining 3.9 grams of titanium dioxide, 9.5 grams of ammoniumparamolybdate, 51 grams of ammonium vanadate and about 22 grams ofammonium sulfate is stirred and heated on a steam bath to 80 C. Theresulting hot mixture together with 250 cc. of 0.16 inch pellets areslowly mixed together until the pellets are uniformly coated and appeardry. The coated pellets are air dried.

The metals in the catalyst mixture prepared in Examples II and III arepresent in the propontion of 81 atomic percent vanadium, l0 atomicpercent molybdenum and 9 atomic percent titanium.

The coated particles described in Examples I and III can be calcined at300 to 600 C. in a muffle furnace to convert the salts of vanadium andmolybdenum to their oxides and charged to a fixed bed such as convertertubes fitted with an inlet charging line for, the feed mixture ofbenzene and oxygen containing gas and a discharge line for the gaseousoxidation products. Or the dried coated particles can be charged to sucha fixed bed and heated to a temperature of from about 300 C. to about600 C. while passing air, generally preheated air, through the bed ofcoated particles.

EXAMPLES IV TO XI Fused silica-refractory glass 0.16 inch pellets coatedas described in Examples 1 to III are charged to a multitu-be converter.All the converter tubes are surrounded by a heated, thermostaticallycontrolled bath. A feed line is connected to the top of the convertertubes and a discharge line is connected to the bottom of the tubes andvented to the atmosphere. 400 C; and maintained at that temperatureWhile air is passed through the catalyst mass to convert the metal saltsto their oxides. Thereafter the temperature of th'e'bath is adjusted tothe desired temperature and a mixture of air and benzene vapor ischarged to the converter tubes and the discharge line is now connectedto a water absorption system to scrub maleic anhydride out of thedischarge gases.

Tabulated in Table I below are the results of operation of the abovedescribed vapor phase oxidation of benzene to maleic anhydride carriedout at different temperatures and ratios of air to benzene but at asubstantially constant rate of flow of gaseous feed per volume ofcatalyst and at a substantially constant head pressure.

T able I VAPOR PHASE CATALYTIC OXIDATION OF BENZENE WITH A'IR IN THEPRESENCE OF MIXTURE OF OXIDES OF V, Mo AND Ti [Atomic percent: 81% V,10% Mo, 9% Ti] Bath 0.11m. Weight Example Number Temp., Alr per 1b.Yield 1 C. Benzene 1 Catalyst of Example III. All other catalysts are oftype described in Example I and ch Basied on pounds of maleic acidrecovered per pounds of benzene arge The bath is brought to about Incontrast to the above, the use of porous catalyst masses comprising thesame type of fused silica-refractory glass particles coated withcatalysts consisting of or consisting essentially of oxides of vanadiumproduces optimum yields at 460 C. which even for an initial operatingperiod averages at least about 10% lower and furthermore the yield dropsafter prolonged operation to about an average of at least 30% lower at460 C.

EXAMPLES XII to XVI Porous catalyst masses whose coatings contain theatomic percentage of the metals as shown in Table II below, wereprepared on particles of an inert carrier of a mixture of silica andrefractory glass which fuses at a temperature above 600 C. Thesecatalyst compositions were prepared according to the method described inExample I.

Table II Atomic Percent Metals in Oxide Mixture Example Number VanadiumMolyb- Titanium denum EXAMPLES XVII TO XXI The catalyst masses ofExamples XII to XVI when used in tube converter for the vapor phaseoxidation of benzene as described in Examples IV to XI gave the resultsshown in Table III below wherein the operating conditions are alsotabulated as in Table I.

Table III VAPOR PHASE OXIDATION OF BENZENE WITH CATALYST OF VARIOUSRATIOS V, Bio and Ti OXIDES The process of Examples IV to XI is repeatedwith the catalyst mass described in Example Iexcept that the henzene airmixture is fed to the converter tubes under about 50 pounds gagepressure instead of the 6 pounds pressure. The weight yield of maleicacid from this process is greatly superior to that obtained withcatalysts consisting of or consisting essentially of vanadium oxideemployed under the same conditions.

The oxidation process described in the preceding examples employing thecatalyst of this invention has been carried out continuously under theconditions set forth therein for many thousands of hours withoutexperiencing a decrease in rate of production. For example, whencatalyst masses comprising a carrier impregnated with a catalystcomprising or comprising essentially of oxides of vanadium are employed,the average weight yield of maleic acid over a period of severalthousands of hours is only about 30 with initial operating yields in therange of 70 to 85.

The process of this invention has been described in terms of the use ofmulti-tube catalyst chambers. The tubes in such chambers can be from 0.5inch to 3 inches or more in diameter and from 1 foot to 10 feet inlength. However, the use of the catalyst mass and the practice of thisinvention is not limited to the use of multi-tube catalyst chambers.'For the present invention can be practiced employing the novel catalystdisclosed herein in a converter employing a fluid catalyst ashereinbefore disclosed or in single or multiple pass tray converters. Insuch tray converters the air or oxygen containing gas is pre-heated toabout operating temperature, passed through a benzene carburetor andthen passed through a porous catalyst mass in a fixed bed 10 to 36inches deep and 10 to 30 feet in diameter at a head pressure of from 0.1to 3 pounds per square inch and at a how rate of 4,000 to 6,000 c.f.m.or more. The operation of such a tray converter is more fully describedin the following example.

EXAMPLE XXIII Coated and impregnated inert particles having a coatingprepared as described in Example III are charged to a tray converter toa depth of 24 inches on top of a punched plate at the bottom of acylindrical catalyst chamber 10 feet in diameter and 36 inches highhaving a reducing section of frustum shape attached to the top andbottom thereof. Each of said reducing sections terminating at a diameterto accommodate a twelve inch duct. Air at a velocity of about 4,800c.f.m. is blown through a preheating chamber where it is heated to about430 C. and then passed through the catalyst bed from the top thereof toconvert the metal salts to oxides of the metals. The spent gasdischarging from the bottom of the converter is vented to theatmosphere. The catalyst mass is burned in in this manner for 12 to 30hours. Thereafter a portion of the hot air is carbureted with benzene,mixed with the remainder of the air, and passed down through thecatalyst bed. The temperature of the supply air is gradually reduced asthe benzene fed is increased to maintain the catalyst bed temperature atabout 300 C. to about 500 C. Although the oxidation process is highlyexothermic, a sufiicient amount of the heat of reaction is dissipatedthrough radiation losses so that the reaction is readily controlled.

The gaseous mixture discharging from the catalyst bed is conducted to aheat exchanger, to preheat the feed air to be carbureted with benzene,and then is conducted to a water scrubber where the maleic anhydride inthe gaseous mixture is recovered as an aqueous solution of maleic acid.The weight yield of maleic acid from a process such as described abovewill be in the range of to or higher based on the benzene charged.

The unoxidized benzene can be recovered from the gaseous mixture andrecycled, if desired. However, a single pass tray converter as describedabove may be operated to produce only a very small amount of unoxidizedbenzene so that the gases discharging from the scrubber can be safelyvented to the atmosphere.

Tray converters having a shallower catalyst bed and/or having a smallerdiameter than that described above can be used in a multipass systemwhere the discharge gases from the first converter after passing througha heat exchanger are passed down through a second catalyst bed. Thenumber of catalyst chambers employed will, of course, depend upon theefiiciency of each bed and the economics of achieving a high weightconversion of benzene.

EXAMPLE XXIV An alkaline paste is prepared as described in Example I sothat the metals present are in the proportion of 81 atomic percentvanadium, 10 atomic percent molybdenum and 9 atomic percent titanium.The resulting mass is placed in an oven, dried and then ground into fineparticles.

These catalyst particles are charged to a fluid catalyst chamber andheated with a stream of hot air to convert the metal salts in thecatalyst to their oxides and thereafter are used as a fluid catalyst forthe oxidation of benzene in admixture with air (500 c.f.m. per pound ofbenzene) at temperatures in the range of 350 C. to 450 C. Theconversions of benzene to maleic acid are substan- I H II tiallyequivalent to those obtained in the examples illustrating this inventionhereinbefore appearing. Similar results are obtained when the fluidcatalyst is prepared by mixing the above-described alkaline paste withpumice (200 mesh) and then subjecting the resulting mass to the dryingand grinding operations.

EXAMPLE XXV An alkaline paste is prepared as described in Example I sothat the metals present are in the proportion of 81 atomic percentvanadium, 10 atomic percent molybdenum and 9 atomic percent titanium. Tothis past there is added about 250 cc. of quartz fragments having aparticle size of from A; to inch. The resulting mass is placed on asteam bath and stirred slowly until the fragments are coated and appeardry. Thereafter the coated fragments are air dried.

EXAMPLE XXVI An alkaline paste is prepared as described in Example I sothat the metals present are in the proportion of 81 atomic percentvanadium, 10 atomic percent molybdenum and 9 atomic percent titanium. Tothis paste there is added about 250 cc. of alumina particles having aparticle size of from to inch. The resulting mass is placed on a steambath and stirred slowly until the fragments are coated and appear dry.Thereafter the coated fragments are air dried.

EXAMPLE XXV II An alkaline paste is prepared as described in Example Iso that the metals present are in the proportion of 81 atomic percentvanadium, l atomic percent molybdenum and 9 atomic percent titanium. Tothis paste there is added about 250 cc. of diatomaceous stones having aparticle size of from to /2 inch. The resulting mass is placed on asteam bath and stirred slowly until the frag ments are coated and appeardry. Thereafter the coated fragments are air dried.

EXAMPLE xxvin An alkaline paste is prepared as described in Example I sothat the metals present are in the proportion of 81 atomic percentvanadium, 10 atomic percent molybdenum and 9 atomic percent titanium. Tothis paste there is added about 250 cc. of asbestos fibers. Theresulting mass is placed on a steam bath and stirred slowly until thefragments are coated and appear dry. Thereafter the coated fragments areair dried.

The catalyst masses of Examples XXIV to XXVHI can be satisfactorily usedin any suitable converter for the vapor phase oxidation of benzene ashereinbefore described. 1

The catalyst of this invention and the use thereof has been illustratedin the foregoing examples solely in the vapor phase oxidation of benzeneto maleic anhydride. Howe er, as heretofore stated the catalyst of thisinventicn and the process of this invention can be used for theoxidation of other organic materials to maleic anhydride, phthalicanhydride, citracoruc acid and other organic acid anhydrides, organicacids and even for the oxidation of alcohols to aldehydes andmonocarboxylic acids.

To illustrate the use of the catalyst of this invention and the processof this invention for the oxidation of other organic materials thefollowing examples are presented. In these examples the catalystcomposition described in Example I was coated on the carrier particles,either of the silica-refractory glass type hereinbefore described orsmall shaped metal pieces so shaped as to form a porous bed for thecatalyst contact mass. The exception to the use of this catalystcomposition will be noted. The results of the oxidation of these variousmaterials are tabulated and appear in Table IV. In these processes thematerial to be oxidized Was admixed with air as hereinbefore 'describedfor benzene,

Table IV Weight Yield 3 Example Temper- N umber Material Oxidized ature,

C. Maleic Phthalic Acid Anhydrida Naphthalene 370 Ortho-Xylene. 400 do460 Ethy1benzene 380 B be 440 460 345 320 Furfural 330 n-Hexane 420Isoheptane 420 utan 430 30 Isoprene 320 65 Citraconic Acid 1 Catalyst ofExample XII. I 2 Both maleic acid and phthalic anhydride produced. 3Yield in pounds per 100 pounds oxidizable material charged. 7

While this invention has been described with respect to certainembodiments, it is not so limited, and it is to be understood thatvariations and modifications thereof can be made without departing fromthe spirit or scope of the invention.

What is claimed is:

1. In a process of preparing an anhydride selected from the groupconsisting of maleic anhydride and phthalic anhydride by the controlledvapor phase oxidation of organic compounds oxidizable to said anhydride,the step comprising contacting a mixture of an organic chemical compoundoxidizable to said anhydride and an oxygen containing gas at an elevatedtemperature with a catalyst comprising a mixture of oxides of vanadium,molybdenum and titanium in the proportions represented by the atomicpercentages of said metals of from about 50 to about 90 atomic percentvanadium, from about 5 to about 45 atomic percent molybdenum and fromabout 2 to about 30 atomic percent titanium.

2.. In a process of preparing an anhydride selected from the groupconsisting of maleic anhydride and phth-alic anhydride by the controlledvapor phase catalytic oxidation of organic chemical compounds oxidizableto said anhydride, the step comprising passing a mixture of an organicchemical compound oxidizable to said anhydride and an oxygen containinggas at an elevated temperature through a catalyst mass comprising acarrier supporting a mixture of oxides of vanadium, molybdenum andtitanimn in the proportions represented by the atomic percentages ofsaid metals of from about 50 to about 90 atomic percent vanadium, fromabout 5 to about 45 atomic percent molybdenum and from about 2 to about30 atomic percent titanium.

3. In a process of preparing maleic anhydride by the controlled vaporphase catalytic oxidation of benzene, the step comprising passing amixture of benzene and an oxygen containing gas at an elevatedtemperature through a catalyst mass comprising a carrier supporting amixture of oxides of vanadium, molybdenum and titanium in theproportions represented by the atomic percentage of said metals of fromabout 50 to about 90 atomic percent vanadium, from about 5 to about 45atomic percent molybdenum and from about 2 to about 30 atomic percenttitanium.

4. In a process of preparing phthalic anhydride by the controlled vaporphase catalytic oxidation of naphthalene, the step comprising passing amixture of naphthalene and an oxygen containing gas at an elevatedtemperature through a catalyst mass comprising a carrier supporting amixture of oxides of vanadium, molybdenum and tita nium in theproportions represented by the atomic percentages of said metals of fromabout 50 to about 90 atomic percent vanadium, from about 5 to about 45atomic percent molybdenum and from about 2 to about controlled vaporphase catalytic oxidation of benzene, the step comprising passing amixture of benzene and an oxygen containing gas at a temperature of from300 to 600 C. through a catalyst contact mass which comprises an inertcarrier body composed of fused finely divided silica and finely dividedparticles of a refractory glass, supporting a mixture of oxides ofvanadium, molybdenum and titanium in the proportions represented by theatomic percentages from said metals of from 50 to 90 atomic percent ofvanadium, from 5 to 45 atomic percent of molybdenum and from 3 to 15atomic percent of titanium.

6. A process of claim 5 wherein atomic percent vanadium is from 60 to86, of molybdenum is 5 to 30 and of titanium is 8 to 10.

7. A process of claim 5 wherein atomic percent of vanadium is 81, ofmolybdenum is 10 and of titanium is 9.

8. A process of claim 5 wherein atomic percent of vanadium is 62, ofmolybdenum is 30 and of titanium is 8.

12 9. A process of claim 5 wherein the atomic percent of vanadium is85.4, of molybdenum is 5.0 and of titanium is 9.6.

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4. IN A PROCESS OF PREPARING PHTHALIC ANHYDRIDE BY THE CONTROLLED VAPORPHASE CATALYTIC OXIDATION OF NAPHTHALENE, THE STEP COMPRISING PASSING AMIXTURE OF NAPHTHALENE AND AN OXYGEN CONTAINING GAS AT AN ELEVATEDTEMPERATURE THROUGH A CATALYST MASS COMPRISING A CARRIER SUPPORTING AMIXTURE OF OXIDES OF VANADIUM, MOLYBDENUM AND TITANIUM IN THEPROPORTIONS REPRESENTED BY THE ATOMIC PERCENTAGES OF SAID METALS OF FROMABOUT 50 TO ABOUT 90 ATOMIC PERCENT VANADIUM, FROM ABOUT 5 TO ABOUT 45ATOMIC PERCENT MOLYBDENUM AND FROM ABOUT 2 TO ABOUT 30 ATOMIC PERCENTTITANIUM.
 5. IN A PROCESS FOR PREPARING MALEIC ANHYDRIDE BY THECONTROLLED VAPOR PHASE CATALYTIC OXIDATION OF BENZENE, THE STEPCOMPRISING PASSING A MIXTURE OF BENZENE AND AN OXYGEN CONTAINING GAS ATA TEMPERATURE OF FROM 300* TO 600*C. THROUGH A CATALYST CONTACT MASSWHICH COMPRISES AN INERT CARRIER BODY COMPOSED OF FUSED FINELY DIVIDEDSILICA AND FINELY DIVIDED PARTICLES OF A REFRACTORY GLASS, SUPPORTING AMIXTURE OF OXIDES OF VANADIUM, MOLYBDENUM AND TITANIUM IN THEPROPORTIONS REPRESENTED BY THE ATOMIC PERCENTAGES FROM SAID METALS OFFROM 50 TO 90 ATOMIC PERCENT OF VANADIUM, FROM 5 TO 45 ATOMIC PERCENT OFMOLYBDENUM AND FROM 3 TO 15 ATOMIC PERCENT OF TITANIUM.